Privacy signal transmission system

Abstract

A privacy signal transmission system having a transmitter portion and a receiver portion. The transmitter portion digitizes an analog message signal and enciphers the digitized signal into a privacy signal before modulation and transmission to the receiver portion. The transmitter portion also extracts and modulates an analog error signal representative of the digitization error for transmission to the receiver portion. The receiver portion demodulates the digitized privacy signal and analog error signal, and after the privacy signal is deciphered and reconverted to an analog signal it is added to the received analog error to reconstitute the original analog message signal.

What is claimed is: 
     
       1. A privacy signal transmission system comprising: a transmitter including digital pulse modulator means for converting a first analog signal into a first digital signal said digital pulse modulator means including means for converting the first digital signal into a second analog signal, encryption means for converting the first digital signal into a first digital privacy signal, subtractor means for producing a first analog error signal representative of the difference between said second signal provided by analog conversion of the first digital signal and the first analog signal, and transmission means for transmitting a modulated signal in response to the first analog error signal and the first digital privacy signal; and   a receiver including means for receiving the modulated signal including the first analog error signal and the first digital privacy signal to generate a second analog error signal and a second digital privacy signal, decryption means for converting the second digital privacy signal into a second digital signal, digital pulse demodulator means for converting the second digital signal into a third analog signal, and reproduction means for reproducing the first analog signal by adding the second analog error signal to the third analog signal.   
     
     
       2. A privacy signal transmission system as claimed in claim 1, in which the digital pulse modulator means comprises a ΔM modulator. 
     
     
       3. A privacy signal transmission system as claimed in claim 1, in which the transmission means comprises frequency modulator means for frequency-modulating a carrier with the first digital privacy signal, amplitude modulator means for amplitude-modulating an output of said frequency modulator means with the first analog error signal, and means for transmitting an output of said amplitude modulator means. 
     
     
       4. A privacy signal transmission system as claimed in claim 3, in which the receiving means includes an AM detector for generating said second analog signal and an FM discriminator for generating said second digital privacy signal. 
     
     
       5. A privacy signal transmission system as claimed in claim 1, in which the transmission means comprises amplitude modulator means for amplitude-modulating the first digital privacy signal with the first analog error signal, frequency modulator means for frequency-modulating a carrier with an output of said amplitude modulator means, and means for transmitting an output of said frequency modulator means. 
     
     
       6. A privacy signal transmission system as claimed in claim 5, in which the receiving means includes an FM discriminator for generating said second digital privacy signal and an AM detector connected to receive the output of said FM discriminator for generating said second analog signal. 
     
     
       7. A privacy signal transmission system as claimed in claim 1, in which the transmission means comprises means for phase-modulating the first digital privacy signal with the analog signal, frequency-modulating a carrier with the phase-modulated signal, and transmitting said frequency-modulated signal. 
     
     
       8. A transmitter for a privacy transmission system comprising: digital pulse modulator means for converting a first analog signal into a first digital signal, said digital pulse modulator means including means for converting the first digital signal into a second analog signal encryption means for converting the first digital signal into a digital privacy signal, subtractor means for producing a first analog error signal representative of the difference between said second analog signal and said first analog signal, and transmission means for transmitting a modulated signal in response to the first analog error signal and the digital privacy signal.   
     
     
       9. A receiver for a privacy transmission system in which a transmitter transmits a modulated signal in response to a first digital privacy signal and a first analog error signal representative of a first analog signal comprising: means for receiving the modulated signal including said first analog error signal and said first digital privacy signal to generate a second analog error signal and a second digital privacy signal, decryption means for converting the second digital privacy signal into a second digital signal, digital pulse demodulator means for converting the second digital signal into a third analog signal, and reproduction means for reproducing the first analog signal by adding the second analog error signal to the third analog signal.